Project Summary Invasive infections by Aspergillus fumigatus and other Aspergillus species are leading causes of mortality and morbidity among profoundly immunosuppressed hosts. Recently, invasive aspergillosis has been described as a complication of severe influenza infection, predominantly among patients who lack traditional aspergillosis risk factors. Despite an increasing number of case reports of influenza-associated aspergillosis (IAA), the incidence and clinical features of the disease in the United States (US) are unknown. Whereas risk factors for aspergillosis are well described in immunosuppressed populations, they have not been defined for patients with severe influenza. In the largest studies of IAA to date, investigators retrospectively diagnosed the disease in 14%-19% of intensive care unit (ICU) patients with influenza at 7 European hospitals from 2009-16; the mortality rate of IAA was 50%. Comparable incidence has been described in retrospective reports from single ICUs, but rates of Aspergillus superinfections in most multi-center studies of severe influenza have been lower. In the absence of systematic testing for aspergillosis among patients with severe influenza, it is possible that IAA is under- recognized by US clinicians and under-reported in the literature. At the same time, incidence may be overstated in the retrospective European studies by liberal acceptance of serum or bronchoalveolar lavage fluid (BALf) galactomannan as definitive markers of disease. Our objectives in this project are to define the incidence, clinical characteristics, and risk factors of IAA by conducting the first prospective study of the disease in the US. We will employ strict IAA case definitions and systematic serum and BALf galactomannan diagnostic testing of ICU patients with severe influenza. We hypothesize that we will demonstrate rates of IAA in the US that are comparable to those reported in Europe, and that a novel point-of-care galactomannan lateral flow assay (LFA) will demonstrate strong sensitivity and specificity for diagnosing IAA. In aim 1, we will conduct a prospective, observational clinical study of IAA in ICUs at 4 large medical centers from different regions of the US. In aim 2, we will evaluate the performance of serum and BALf galactomannan LFA for diagnosing IAA. Our findings will allow us to develop strategies for rapidly and accurately identifying patients with IAA. This study addresses fundamental gaps in understanding of the epidemiology and clinical aspects of an under-appreciated form of invasive aspergillosis. It will lead to clinical trials in which improved understanding of IAA and its diagnosis are used to guide early antifungal treatment strategies, as well as to future laboratory studies of IAA pathogenesis. The project is feasible due to the multidisciplinary expertise of our collaborative team of pre-eminent physician- investigators. Finally, the study has the support of the US Centers for Disease Control and Prevention and a recently-formed international IAA consortium, relationships that will useful in designing and executing follow-up projects.